To consolidate the soil, or to make foundation piles near structures, or to make anchoring tie rods, and in other similar cases, micropiles are used which are made of steel or of concrete cast in holes made in the ground with suitable equipment.
Making micropiles by casting concrete into the ground contemplates the drilling of the ground with a drilling rod accompanied by a cylindrical covering.
At the end of the drilling rod there is a tool driven by air or by water under pressure.
The outer covering holds back the soil around the hole until the moment of the casting and allows the extraction of the material removed by the tool of the drilling rod during the drilling operation.
The drilling rod and the outer covering are driven into the soil simultaneously. At the end of the drilling operation the drilling rod is extracted, the pile or reinforcement and the concrete are introduced in the covering which is extracted gradually so as to allow the concrete to be perfectly compacted in the hole left by the covering.
Both the drilling rod and the covering are composed of various modular elements which are joined together, usually by screwing, until the necessary drilling length is obtained.
To make micropiles by casting concrete into the ground with a rod and covering, drills are used that are equipped with a mast (or guide or slide) that may be turned in various directions, on which a trolley with a drilling head slides, the drilling rod and/or the covering being applied on said trolley.
At the bottom end of the mast there is a group of vices comprising two pairs of jaws, called bottom vice and top vice, the latter being also called unscrewing vice, overlapping each other and concentric with the path of the trolley, the drilling rod and the covering.
In particular, the top pair of jaws rotates with respect to the mast. In this way the bottom jaws hold the rod or the covering already inserted while the rotating top jaws release the rod and/or covering elements next to them.
These drills permit the creation of holes for micropiles with a drilling rod and covering, but they present a series of inconvenient aspects.
The extraction of the drilling rod and of the covering is entrusted to the head-carrying trolley, which consequently must resist high stress. The advance movement of the head-carrying trolley is ensured by jacks, cables, chains, etc.
The screwing and unscrewing of the modular elements of the drilling rod and of the covering are possible only when the joining point is exactly between the two vices or pairs of jaws, where it is difficult for the operator to determine, both during drilling and during extraction the exact point in which to stop the trolley so that the joining point is exactly between said two vices.
At present for the standard version it is necessary to perform in sequence the operations described below for each element:                1. extract the rod for one module (˜1.5 m) checking that the joining point is between the two sets of jaws;        2. block both vices and turn the upper unscrewing device;        3. disengage the unscrewing device, rotate the module by turning the head;        4. engage the unscrewing device on the module and disengage the head at the top;        5. unscrew the rod from the head and put away the rod;        6. move the head downwards until it screws onto the still semi-fixed module.        
All these operations must obviously be repeated until the drilling device (rod) is completely extracted.
Moreover, these operations must also be performed for the covering.
The studies, stratagems and solutions adopted until now have not led to any acceptable result, sometimes even aggravating the situation.